This invention relates to a method for examining samples of oilfield flowlines. More particularly, the invention method concerns the isolation of a flowline sample without shearing the sample so that a more accurate examination of the flowline sample can be performed.
In the oilfield, production flowlines carry produced fluids from production wells to processing facilities. Because of the nature of oil production, particularly in older fields, and more particularly where fluids have been injected into the reservoir to enhance oil production, the produced fluids contain a large volume of water in proportion to produced oil.
Produced water is more than an inconvenience. The water must be separated from the produced oil. This is generally done with a combination of mechanical oil and water separators and chemical treating. Water treating chemicals are normally injected in the field upstream of mechanical oil and water separators to take full advantage of the natural agitation that occurs in petroleum flowlines. Thus, most of the oil droplet coalescence occurs in flowlines upstream of separators. Flowlines are also commingled from various wells into a common oil and water separator. As a rule, only the overall separation performance of the oil and water separator can be monitored.
Attempts to monitor the water quality of individual flowlines to check on the chemical treatment needed for each individual flowline have failed. If samples are removed from individual flowlines, the coalesced oil droplets shear as they pass through a pressure drop. A measurable pressure drop across a valve of one psi or more can cause substantial shearing. Consequently, samples drawn from flowlines are inaccurate measures of the success of chemical treatment in the flowlines prior to the oil and water separators. In some cases, the sheared samples become reverse oil-in-water emulsions as bad as those existing at the production wellhead prior to chemical treatment in the flowline.